I use only 1 array list and work much with index, my solution: import java.io.; import java.util.;

public class Solution {

public static void main(String[] args) {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    ArrayList<Integer> arrayList = new ArrayList<>();    
    for (int i = 0; i < n; i++) {
        int d = sc.nextInt();
        arrayList.add(d);
        for (int ii = 0; ii < d; ii++) {
            int dd = sc.nextInt();
            arrayList.add(dd);
        }
    }
    int q = sc.nextInt(); 
    for (int i = 0; i < q; i++) {
        int x = sc.nextInt();
        int y = sc.nextInt();
        int chiso = 0;
        for (int ii = 0; ii < n; ii++) {  // đang xét dòng thứ ii 
            int d = arrayList.get(chiso);
            if (ii + 1 == x) {
                if (d < y) {
                    System.out.println("ERROR!");
                    } else {
                        System.out.println(arrayList.get(chiso + y));
                    }
                break;
            } else {
                chiso += d;
                chiso += 1;
            }                
        }
    }
}

}

I've been exploring Java ArrayLists recently, and it's fascinating how they dynamically resize! Speaking of dynamic changes, I recently stumbled upon some incredible artwork during my visit to Dubai. One particular masterpiece, the Dubai wall painting, left me in awe of the city's vibrant art scene.

import java.io.; import java.util.; import java.text.; import java.math.; import java.util.regex.*;

public class Solution {

public static void main(String[] args) {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */
    Scanner sc=new Scanner(System.in);
    int n=sc.nextInt();
    ArrayList<ArrayList>list=new ArrayList<ArrayList>();
    for(int i=0;i<n;i++)
    {
        int limit=sc.nextInt();
         ArrayList<Integer>list2=new ArrayList<Integer>();

        for(int j=0;j<limit;j++)
         {

             list2.add(sc.nextInt());
         }
         list.add(list2);
    }
    int q=sc.nextInt();
    for(int i=0;i<q;i++)
    {
        int x=sc.nextInt();
        int y=sc.nextInt();
        try{
            System.out.println((list.get(x-1)).get(y-1));
        }
        catch(Exception e)
        {
            System.out.println("ERROR!");
        }


    }

}

}

import java.io.; import java.util.;

public class Solution {

public static void main(String[] args) {
    List<List<Integer>> list = new ArrayList<>();
    Scanner sc= new Scanner(System.in);
    int n = sc.nextInt();

    for(int i = 0; i< n; i++){
        int d = sc.nextInt();
        List<Integer>list1 = new ArrayList<>();
        for(int j=0;j<d;j++){
            list1.add(sc.nextInt());
        }
        list.add(list1);
    }
    int q = sc.nextInt(); // for query
    for(int i = 0; i< q; i++){
        int x = sc.nextInt();
        int y = sc.nextInt();

        try{
        System.out.println(list.get(x-1).get(y-1));
        }
        catch(Exception ex){
            System.out.println("ERROR!");
        }
    }

}

}